Traditionally, polymers and commodity chemicals have been prepared from petroleum-derived feedstocks. However, as petroleum reservoirs are rapidly depleting and concomitantly becoming more difficult to access, an exigency to develop renewable or “green” alternative materials from biologically-derived resources has been at the vanguard of much current research, particularly in the role of commercially tenable surrogates to conventional, petroleum-based or -derived counterparts, or for generating the same materials as produced from fossil, non-renewable sources.
One of the most abundant kinds of biologically-derived or renewable alternative feedstock for such materials is carbohydrates. Carbohydrates, however, are generally unsuited to current high temperature industrial processes. In contrast to petroleum-based, hydrophobic aliphatic or aromatic feedstocks with a low degree of functionalization, carbohydrates such as sugars are complex, highly functionalized hydrophilic materials. As a consequence, researchers have sought to produce biologically-based chemicals that originate from carbohydrates, but which are less highly functionalized, including more stable bi-functional compounds, such as 2,5-furandicarboxylic acid (FDCA), levulinic acid, and 1,4:3,6-dianhydrohexitols.
1,4:3,6-dianhydrohexitols (also referred to herein as isohexides) are derived from renewable resources from cereal-based polysaccharides. Isohexides embody a class of bicyclic furanodiols that derive from the corresponding reduced sugar alcohols, namely D-sorbitol, D-mannitol, and D-iditol, respectively. Depending on chirality, the three isomers of the isohexides are: A) isosorbide, B) isomannide, and C) isoidide, respectively, the structures of which are illustrated in Scheme 1.

The conventional chemistry used for dehydration of sugar alcohols to produce dianhydrohexides generates undesired byproducts. The high cost and complexity of current methods for the separation of isohexides from the numerous byproducts makes the development of less expensive and simpler alternatives highly desirable. Hence, a process which can enhance greater conversion and higher yield of the desired product, as well as lessens amount of byproducts would be welcome.